People inspect the damage at a site hit by airstrikes in the rebel-held city of Idlib, Syria, Feb. 7, 2017. Photo: Reuters / Ammar Abdullah.

US-led war planes killed an Islamic State leader on Sunday in Syria responsible for executing hostages including an American, Washington’s envoy to the coalition fighting the jihadist group said.

“Earlier today, coalition air forces conducted precision strikes against a number of ISIS leaders in southeast Syria. Those targeted included Abu al-Umarayn,” Brett McGurk said in a Tweet late on Sunday.

Abu al-Umarayn was responsible for killing several prisoners including the U.S. aid worker Peter Kassig, who was captured by the group in Syria and beheaded in 2014, McGurk said.

The strike in the Badia desert in eastern Syria killed “several other ISIS members”, said Colonel Sean Ryan, spokesman for the US-led coalition against Islamic State.

Abu al-Umarayn “had given indications of posing an imminent threat to coalition forces,” Ryan said.

Late on Sunday, Syrian state media reported that the United States had fired missiles at Syrian government positions in the desert in eastern Syria. Ryan said the coalition did not fire at any Syrian forces.

Islamic State has lost almost all the territory in Iraq and Syria where it once declared a caliphate, including its two main cities of Mosul and Raqqa last year.

The US-led coalition is supporting a group of Kurdish and Arab militias assaulting the last Islamic State territory in eastern Syria near the Iraqi border.

The Syrian army last month said it had completed its own operation against an Islamic State pocket in southern Syria.